1. Field of the Invention
The present invention relates to photoresist polymers and photoresist compositions containing the same, and in particular to photoresist polymers and compositions that are suitable for photolithography processes employing KrF, ArF, EUV and preferably 157 nm light sources like VUV.
2. Description of the Prior Art
Recently, chemical amplification-type DUV photoresists have been investigated in order to achieve high sensitivity in minute image formation processes for preparing semiconductor devices. Such photoresists are prepared by blending a photoacid generator and matrix resin polymer having an acid labile group.
In a photolithography process, an exposure of photoresist to light of a particular wavelength generates an acid from the photoacid generator that is present in the photoresist. This acid causes the main chain or the branched chain of the resin to decompose or become cross-linked. In addition, the acid removes the acid labile group and changes the polarity of the photoresist in the exposed region. This polarity change creates a solubility difference between the exposed portion and the unexposed portion in a developing solution, thereby allowing a pattern formation. The resolution of the pattern that is formed depends on the wavelength of the light sourcexe2x80x94i.e., in general, a shorter wavelength allows formation of more minute patterns.
In general, a useful photoresist (hereinafter, abbreviated as xe2x80x9cPRxe2x80x9d) has a variety of desired characteristics, such as excellent etching resistance, heat resistance and adhesiveness. In addition, a photoresist should be easily developable in a commercially readily available developing solution, such as 2.38% aqueous tetramethylammonium hydroxide (TMAH) solution. Furthermore, it should provide a good pattern formation using a light source of wavelength of 157 nm. However, it is very difficult to synthesize a photoresist polymer that satisfies all of these desired characteristics. For example, a polymer having a polyacrylate polymer backbone are readily available, but it has poor etching resistance, difficult to develop and impossible to obtain a good minute pattern due to its poor transmittance at wavelength of 157 nm.
FIG. 1 shows transmittance of several resins at wavelength near 157 nm. For example, PVP (poly vinyl pyrrolidine) which is typically used for wavelength of 248 nm (KrF light source), and PMMA (poly methyl methacrylate) which is typically used for wavelength of 193 nm (ArF light source) showed relatively poor transmittance at 157 nm. If these resins, which have poor transmittance at wavelength of 157 nm, are used for a pattern formation with 157 nm wavelength light, most of the light can not reach the lower portions of the PR resulting in a poor or no pattern formation (see FIG. 2a). In addition, even if the light cm penetrate to the lower portions of the PR, the difference in the intensity of light reaching the upper portion and the lower portion of the PR will cause a large gap in CD of both portions of the PR, thus creating line patterns with a severe slope, i.e., CD of the upper portion of PR will be relatively small and CD of the lower portion will be relatively large (see FIG. 2b). Hence, the shape or the pattern formed using these PR at 157 nm wavelength is not suitable for fabricating a semiconductor element.
An object of the present invention is to provide novel photoresist polymers having a good or excellent transmittance at 157 nm wavelength, etching resistance, adhesiveness and photosensitivity, and a process for preparing the same.
Another object of the present invention is to provide photoresist compositions comprising the PR polymers described above, and a process for preparing the same.
Still another object of the present invention is to provide a semiconductor element produced by using the photoresist composition.